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The cosmos – <I>before</I> the big bang

How did the universe begin? The question is as old as humanity. Sure, we know that something like the big bang happened, but the theory doesn’t explain some of the most important bits&colon; why it happened, what the conditions were at the time, and other imponderables.

Many cosmologists think our standard picture of how the universe came to be is woefully incomplete or even plain wrong, and they have been dreaming up a host of strange alternatives to explain how we got here. For the first time, they are trying to pin down the initial conditions of the big bang. In particular, they want to solve the long-standing mystery of how the universe could have begun in such a well-ordered state, as fundamental physics implies, when it seems utter chaos should have reigned.

Several models have emerged that propose intriguing answers to this question. One says the universe began as a dense sea of black holes. Another says the big bang was sparked by a collision between two membranes floating in higher-dimensional space. Yet another says our universe was originally ripped from a larger entity, and that in turn countless baby universes will be born from the wreckage of ours. Crucially, each scenario makes unique and testable predictions; observations coming online in the next few years should help us to decide which, if any, is correct.

Not that modelling the origin of the universe is anything new. The conventional approach is to take the laws of physics and extrapolate backwards from the present. From observations dating back to the 1920s, we can see that galaxies are moving …